^Polytechnic Association Proceedings. 925 



li3'drogen. Sulphuretted hydrogen gas and a hydrate of silica are 

 formed, both of which are soluble in water, and easily carried along 

 by steam. The upper cavities, mostly filled with water impreg- 

 nated with carbonic acid, which in itself is a great solvent and 

 combining medium for metallic oxides, such as iron, copper, and 

 others (all of which, no doubt, exist dissolved in this water), are 

 suddenly broken into by these water vapors, carrying the hydrated 

 silica and sulphuretted hydrogen with them, and the oxides hydrates, 

 and other metallic solutions are broken up; the sulphur of the 

 sulphuretted hydrogen seizes upon the metals, forms therewith 

 sulphides, and the whole mass is forced upward, together with the 

 liquid quartz. The hydrated silica carrying the heavier sulphuretted 

 metals in the center, comes in contact with the cool atmosphere and 

 the cold sides of the crevices, and a gelatinization and gradual 

 crystalization takes place — the sulphm-ets crystalizing in the quartz. 



I can reproduce, artificially, in a small way, what nature has done 

 on a large gigantic scale. I can heat granite to a white heat, expose 

 it to the vapors of bisulphide of carbon, then treat the sulphides 

 resulting therefrom by steam, and carry the hydrate of silica and 

 sulphuretted hydrogen into a basin containing carbonate of iron or 

 other metallic solution, w'hen the silica will be seen to gelatinize 

 slowly, and the sulphurets of iron or copper crystal ize in the silica. 



Experiments which I have made in my own laboratory have led 

 me to the following: 



1. That gold exists in nature in two distinct allotropic conditions. 

 In a crj'staliue state, withstanding the action of oxidizing agents 

 under ordinary conditions, and in an amorphous, and oxidizable 

 form. Plumbago and lampblack may illustrate this idea. The 

 former is heavy, a good conductor of electricity, and has all the 

 appearance of a metal, while the latter, the lampblack, is easily 

 oxidized, is light, is a non-conductor of electricity, and is amorphous. 



2. That in sulphurets the gold is mostly present in both modifi- 

 cations, and may sometimes be found in a chemically combined 

 state. 



I will here cit€ a curious experiment, which gives a fair illustra- 

 tion of what I say: 



A quantity of finely pulverized sulphurets from a rich mine in 

 Colorado, Montana, or California is, at fii'st, carefully treated in a 

 close vessel, with mercury vapors, then cooled and washed, the 

 mercury separated, and the resulting quantity of gold weighed. 

 The sulphurets, after having been thus treated, are then mixed with 



